A Novel Compound Targeting Kv7.2/3 Channels Relieves Inflammatory and Neuropathic Pain

Encoded by Kv7.2/Kv7.3 subunit assembly, M-channels generate sub-threshold voltage-gated K+ currents that regulate neuronal excitability. Inour quest to target neuronal M-channels, we previously designed noveldiphenylamine carboxylates that are powerful Kv7.2 channel openers. These drugs stabilize the Kv7.2 channel open state by interacting with its voltage sensing domain (VSD). Using the same structural framework, we designed a novel molecule, NH34, to test its activity on neuronal excitability and probe its potency in vivo on inflammatory and neuropathic pain. In transfected CHO cells, NH34 significantly increased Kv7.2 currents, by producing a hyperpolarizing voltage shift of the activation curve (EC50 = 17.5 µM). Interestingly, two S4 mutants, R198A and R207W significantly decreased the opener potency of the drug, suggesting that NH34, like NH29, may interact with the VSD of Kv7.2. NH34 preferentially acts as an opener of Kv7.2 and Kv7.3 channels. NH34 was ineffective on Kv7.4 and Kv7.5 but produced a significant inhibition of TRPV1 cation channels. In CA1 pyramidal neurons from rat hippocampal slices, NH34 reduced the spike discharge frequency evoked by injection of depolarizing current. NH34 significantly depressed the slope of field epsp and the fiber volley amplitude recorded extracellularly in the CA1 pyramidal region following stimulation of the Schaeffer collaterals. NH34 reduced the frequency of evoked spike discharge in dorsal root ganglion neurons. In vivo, NH34 (3-30 mg/kg p.o) significantly relieved the hyperalgesia evoked by mechanical pressure of the paw in a rat model of inflammatory pain. Similarly, NH34 (3-30 mg/kg p.o) was very efficient in alleviating the hyperalgesia evoked by mechanical pressure or cold allodynia in a Seltzer rat model of neuropathic pain. In all, the data suggest that NH34 is a very promising drug template for treating inflammatory and neuropathic pain.